The nanoscale science and engineering have shown great promise for the fabrication of novel nano-biosensors with faster response and higher sensitivity than that of planar sensor configurations, due to their small dimensions combined with dramatically increased contact surface and strong binding with biological and chemical reagents which could have important applications in biological and biochemical research, as well as in environmental monitoring and protection.
ZnO nanostructures have many advantages. As disclosed in U.S. patent application Ser. No. 10/243,269, nanotip arrays made with semiconductive, insulating or conductive ZnO can be fabricated in a controlled manner to produce tips with a uniform size, distribution and orientation. The ZnO nanotips are made using our chemical vapor deposition (CVD)-based method in a simple process at relatively low temperatures as disclosed by S. Muthukumar*, H. Sheng*, J. Zhong*, Z. Zhang*, N. W. Emanaetoglu*, Y. Lu, “Selective MOCVD Growth of ZnO Nanotips”, IEEE Trans. Nanotech, Vol. 2, n. 1, pp. 50-54 (2003), giving ZnO nanostructures a unique advantage over other wide bandgap semiconductor nanostructures, such as gallium nitride (GaN) and silicon carbide (SiC). Furthermore, through proper doping and alloying, ZnO nanotips can be made as semiconductor with different doping level, piezoelectric, transparent and conducting, and magnetic, thus having multifunctional sensing applications.
Recent advances in genetic sequencing methods are leading to an explosion in the area of biotechnology. Many emerging areas of biotechnology are based upon highly-parallel methods for sequencing and detecting DNA, RNA, and proteins. Many of these areas could benefit greatly by leveraging the emerging nanotechnology, but applying it to develop and utilize new analytical tools for biochemical analysis. A need exists to provide novel biological and biochemical sensors, which have higher sensing efficiency and multiple functionality, thereby having significant advantages in comparison to the existing sensor technology.
ZnO is emerging as a major wide band gap semiconductor material. It also possesses unique multifunctional properties, which are critically important for new sensor technology. ZnO nanostructures have become one of the most important and useful multifunctional nanostructures. It can be grown at low temperature on various substrates. ZnO nanostructures have been found broad applications in optoelectronics, electronics, catalysts, and especially, for high sensitivity sensor technology.
TFBAR is one of the key devices for RF IC, signal processing, frequency control, and sensors, which offers advantages, such as small size, high frequency operation, low insertion loss, and lower power consumption. They are also attractive for the capability of monolithic integration with Si ICs, leading to miniaturization and reducing cost. The integration of ZnO nanotips with TFBAR technology will lead to the new nanosensors, particularly wireless sensor devices inheriting advantages from both technologies. It can operate at the high frequency range (in GHz range).
On the other hand, QCM has been widely used as the sensor devices for various gas detection, immunosensor, DNA biosensor, and drug analysis in many areas of biological, food, environmental and clinical analysis. It has many advantages, such as high-quality (Q) factor, typically 10,000 to 100,000 at room temperature, which leads to the high sensitivity, low-cost and commercially availability. The integration of ZnO nanotips with QCM leads to another new nanosensors inheriting advantages from both technology. It operates at the relatively low frequency range (1-100 MHz range).
Such novel sensors can be used to detect various gas and biological molecules interactions of DNA-DNA, DNA-RNA, protein-protein, and protein-small molecules, for examples, glucose and uric acid detection. Some of new commercial applications include:
(i) New methods for the prevention, diagnosis and treatment of diseases;
(ii) Detection of gas phase and liquid phase chemical and biochemical agents, and hazardous chemicals for homeland defense against bioterrorism activities following the 9/11 attacks;
(iii) Environmental monitoring and protection due to its multifunctional material properties (semiconductor, piezoelectric, transparent and conductive, etc.). The nano-patterned and uniformly distributed ZnO nanotip arrays on TFBAR and QCM sensors can efficiently and accurately detect the presence of targets in a given sample due to affinity between molecules and nanotips.
Some of the advantages presented by the sensors according to the present invention include the following:                (i) ZnO as metal oxide semiconductor is an excellent sensing material. It has been used to sense various gaseous species, such as NOx, CO, H2, NH3, etc. When it is integrated to QCM and TFBAR, it dramatically extends these two popular BAW sensor technologies, and enhances the performances.        (ii) ZnO can be grown as thin films or as nanoscale structures. Nanoscale sensors show great promise, as they have faster response and higher sensitivity than planar sensor configurations, due to their smaller dimensions combined with dramatically increased sensing surface and strong binding properties. We have demonstrated that ZnO nanotips can greatly enhance DNA and protein immobilization.        (iii) Wettability control of ZnO nanostructured sensor surfaces can greatly reduce the liquid consumption and further enhance the sensitivity.        (iv) ZnO is a multifunctional material, which is excellent for sensor technology. It is a wide bandgap semiconductor. With proper doping, ZnO can be made as semiconductive, transparent and conductive, piezoelectric, or ferromagnetic. It has excellent optical, electrical and acoustic properties. The integration of some or all of these functions into one single sensor platform, or by arraying the different types of ZnO nanosensors into a chip will enhance the sensitivity and accuracy.        (v) It can be used for both gas and liquid phase sensing. It also can be integrated with microfluidics, especially useful for future sensor-on-chip and lab-on-chip technologies.        (vi) It can be used for the low-power and wireless sensor devices.        (vii) ZnO nanotips and tip-arrays can be grown and patterned at the surface of semiconductors, (such as Si, GaN, etc.), glass, SiO2 film, metals and single crystal substrates (e.g. LiNbO3, quartz, Al2O3, etc.) at low temperature (˜400° C.). The direct integration of ZnO nanotips with popular QCM and TFBAR offers advantages of the novel sensor technology: excellent manufactability and the large-scale production.        
In contrast to conventional sensor technologies, the invented sensor integrates QCM and TFBAR with ZnO nanostructures. Therefore, this type of new sensors possess advantages of both technologies of QCM and TFBAR, (such as ease and low cost of fabrication, being rugged, and convenience of operation), and of nanoscale sensors (such as high efficiency, accuracy, and rapid response).
In addition, unique multifunctional sensing mechanisms enhance measurement reliability and accuracy operating in gaseous, as well as in liquid environments. It is feasible for integration to make system-on-a-chip or lab-on-a-chip technology. Compared to planar sensors, nanoscale sensors will respond significantly faster with substantially higher sensitivity.
Furthermore, due to the unique chemical properties high-density ZnO nanotip arrays will be used for the diagnostic kits and flow-through systems. This represents an opportunity for development of miniaturized cost-effective devices for clinical applications.